The therapeutic function of long-chain, highly unsaturated carotenoids of higher plants is becoming increasingly well understood. The conjugated polyene chromophore of such molecules determines not only the carotenoids light absorption properties, and hence color, but also the photochemical properties of the molecule and consequent light harvesting and photoprotective action. The polyene chain is also the feature mainly responsible for the chemical reactivity of carotenoids towards oxidizing agents and free radicals, and therefore for any antioxidant function.
Carotenoids having the above described features, include but not limited to, lutein, zeaxanthin, beta carotene and lycopene.
Lycopene is an open-chain unsaturated carotenoid that confers red color to tomatoes, guava, rosehip, watermelon and pink grapefruit. This compound is non-polar and lacks any type of interaction with water. Thus, when introduced into water, it forms granules. Lycopene exhibits the highest physical quenching rate constant with singlet oxygen and its plasma level is slightly higher than that of beta carotene. Epidemiological evidence revealed that lycopene and the like exert a protective action against certain types of diseases, including cancer, heart disease and other diseases which have radical or oxidant involvement.
One of the major difficulties in formulating carotenoids is their lack of solubility and homogenous dispersibility in water and low solubility in many organic solvents. The low solubility of carotenoids which is related to their high lipophilicity and rigid structure, leads to low bioavailability of the compound. It is thus suggested by the present invention to make use of liposomal delivery systems to improve the bioavailability of carotenoids.
It has well been established that liposomes are suitable delivery vehicles for parenteral, peroral, topical and inhalation administration of drugs. Liposomes, which are biocompatible, may improve for an active substance the formulability, provide prolonged release, improve the therapeutic ratio, prolong the therapeutic activity after each administration, reduce the need for frequent administration, reduce the amount of drug needed and/or absorbed by target tissue.
Active substances, such as drugs, may be contained within the liposome (in the intraliposomal aqueous phase) or entrapped within the lipid bilayer. In the later case, the drug may be positioned parallel to the acyl chains or in the bilayer center. Further, the active substance may be bound to the outer surface of the liposome.
Loading of drugs into liposomes has proved to be a measure of their utility. If there is a poor loading, there is a great loss of the active drug and the use of the liposomes as the pharmaceutical vehicle becomes uneconomical.